The present invention relates to industrial organic synthesis, specifically to production of phenol and acetone by the cumene method.
A well-known method for the production of phenol and acetone by oxidation of cumene with atmospheric oxygen, followed by the acid-catalytic decomposition of cumene hydroperoxide permits both end products to be produced with high yield (see, for example, Kruzhalov B. D., Golovanenko B. N., Combined Production of Phenol and Acetone, Moscow, Goskhimizdat, 1964, or Kirk-Othmer Encyclopedia of Industrial Chemistry). The method is widely used to produce these products, and is the principal technique used in world practice.
Methods are known for producing phenol and acetone in which, to reduce the yield of phenol tar, cumene oxidation products containing cumene hydroperoxide (CHP), cumene, and dimethylphenylcarbinol (DMPC) cleavage process in the presence of sulfuric acid. In the first stage, at a temperature of 55 to 80° C., most of the CHP (97 to 99%) is decomposed and dicumyl peroxide (DCP) is synthesized from DMPC and CHP. In the second stage, acetone is added at a temperature from 80 to 146° C. to the obtained reaction mixture containing phenol, acetone, dimethylphenylcarbinol (DMPC) and dicumyl peroxide (DCP). The addition is made in an amount of 1.5 to 1.8 times the original concentration of acetone. Water is also added. In some cases the acid is partially neutralized with ammonia before the second separation stage in order to ensure optimal acidity of the catalyst. Breakdown of DCP formed in the first stage, decomposition of the remaining CHP and dehydration of the remaining DMPC occur here at a temperature from 80 to 146° C. (See, for example, Russian Patent Nos. 2068404, 2121477, 2142932.)
These methods significantly reduce the amount of formed byproducts in comparison with decomposition in one stage (the yield of tar is 25 kg/t of phenol), whereas the amount of formed byproduct (hydroxyacetone) remains at a high level (and sometimes increases).
Hydroxyacetone is a precursor to 2-methylbenzofuran, which is difficult to separate from phenol and which causes a deterioration in the color indices of the commercial phenol. Elimination of hydroxyacetone from phenol by alkaline treatment complicates the process (Vasil'eva I. I., Zakoshanski V. M., Petroleum Processing and Petrochemistry, St. Petersburg, “Giord”, 2005, page 344).
The yield of hydroxyacetone during decomposition of CHP to phenol and acetone is reduced by running the reaction in excess phenol. (See, for example, Russian Patent No. 2291852 and U.S. Pat. No. 7,109,385.) However, these methods propose that part of the commercial product (phenol) that has already passed through all separation stages be returned to the CHP decomposition stage, which undoubtedly leads to a reduction in the output of the unit because of an increase in the load on the phenol separation and purification system.
The method closest to the proposed method for the decomposition of CHP is a decomposition method that is accomplished in two stages. (See, for example, Russian Patent No. 2142932.) The prior art process is run in three serially connected mixing reactors in the first stage and in a displacement reactor in the second stage. In the first stage, CHP decomposition is carried out under conditions that are close to isothermal at a temperature of 47 to 50° C. and a catalyst concentration (sulfuric acid) of 0.018 to 0.20 wt. % by additional dilution of the reaction mass with acetone in an amount equal to 5 to 8 wt. % relative to the amount of supplied CHP. Almost all the CHP reacts, and DCP is formed from part of the CHP and DMPC.
In the second stage, the process is run while sulfuric acid is partially neutralized with ammonia to form ammonium hydrosulfate at a temperature of 120 to 146° C. A certain amount of water is added, as needed. The concentration of sulfuric acid is 0.09 to 0.10 wt. %. Decomposition of CHP and DCP occurs in a reaction medium containing phenol and acetone. These are formed from CHP and the additionally introduced acetone.
Shortcomings of the prior art method include the significant amount of hydroxyacetone in the obtained phenol. According to the inventors, this amount constitutes 1300 ppm in the reaction mass resulting from the decomposition of CHP, which significantly reduces the quality of the compound (as described in a report of the inventor of the prior art method at the conference “Outlook for Development of Chemical Processing of Fossil Fuels”, KHPGI-2006, 12-15 Sep. 2006, Saint Petersburg; “Khimizdat”, Saint Petersburg, 2006, page 130). Another shortcoming is the need for the partial neutralization of sulfuric acid with ammonia, which complicates the process and process control.